Whenever we reflect on the horror of Nov. 22, 1963, we mourn not only the murder of a graceful and inspiring leader but†also†a steady ebbing in the years thereafter of our faith in what we could achieve through public life and common endeavor.

It tells us a great deal about the meaning of†John F. Kennedy in our history that liberals and conservatives alike are so eager to pronounce him as one of their own.

The evidence points to a man who began his political career as something of a conservative and ended it as more of a liberal -- cautious, skeptical and pragmatic, but a liberal nonetheless. His important speeches late in his presidency about civil rights and nuclear disarmament remain lodestars for American progressives, and the philosophical trajectories of his brothers Robert and Ted no doubt further shape assessments of Kennedy’s legacy.

But more important than settling the question of who has a fair claim on JFK is the reason why all sides want to get right with him: He has come to represent a time of widespread national confidence in our country’s possibilities. The year 1963 dawned, as Andrew Kohut of the Pew Research Center has noted, with 82 percent of the country believing that the power of the United States would increase.

Kennedy, for all his cool, ironic detachment, showed a genuine passion for public service and, yes, for politics itself. It is a passion we have never again experienced in quite the same way.

His 1960 campaign was premised on impatience with the quiet satisfactions of the Dwight Eisenhower years. Kennedy’s emphasis on the “vigor” of a new generation ready for responsibility set the tone for social upheavals and generational conflicts later in the decade that would probably have surprised him. For all his emphasis on change and new departures, Kennedy was speaking for a deep consensus in the country (Ike was part of it) about the meaning of our triumph in World War II and our success in overcoming the damage done by the Great Depression.

As Robert Reich has written, these were large social undertakings in which all Americans felt they had a stake. As a result, “society was not seen as composed of us and them; it was the realm of we.” A nation inspired by this capacious understanding of “we” could not escape its rendezvous with civil rights and social justice. After Kennedy’s death, Lyndon Johnson harnessed his formidable political skills to a tide that was with him.

Back then, we were, as always, critical of politicians, but we were at least open to the idea that politics could be ennobling. Compare the hardheaded vision of politics in the Mark Halperin and John Heilemann volumes “Game Change” and “Double Down” with Theodore H. White’s heroic account of Kennedy’s election in “The Making of the President 1960.” Perhaps White was a bit starry-eyed, but the popularity of his book suggested that many shared his sense of romance.

Page 2 of 2 - How many politicians will ever again defend their line of work with the enthusiasm Kennedy brought to a 1957 commencement address at Syracuse University? Politics, he said, “has become one of our most neglected, our most abused and our most ignored professions.” Yet he urged the next generation to embrace the “compromises and majorities and procedural customs” of political life and to “offer to the political arena ... the benefit of the talents which society has helped to develop in you.”

Kennedy’s defense of politics and his celebration of service went hand in hand with his assumption that individual success found its roots in social arrangements that made prosperity and achievement possible. No wonder so many heeded his call to join the Peace Corps and to flock to Washington. Imagine a time when working for government seemed as exciting as joining the tech industry does now. Imagine when Wall Street was sleepy and the public sphere was thrilling.

After the assassination, the legendary columnist and Kennedy admirer Mary McGrory declared disconsolately to Daniel Patrick Moynihan, then a Kennedy aide: “We’ll never laugh again.” Moynihan replied: “Mary, we will laugh again. It’s just that we will never be young again.”

Youth has its drawbacks. There was hubris on the New Frontier, and a naivete beneath its relentless realism. The technocrat in Kennedy had an outsized faith in the capacity of experts to crack overcome previously intractable problems. But as a nation, we could use a dose of that youthful self-assurance. We miss it still.